Manufacture of explosives



Patented May 2, 194.4

, 2,347,660 MANUFACTURE or ExPaosrvns Jerome G. Burtle, GodfreyTownship, Madison County, 111., assignor to Western, Cartridge Company,East Alton, 111., a corporation of Dela- No Drawing. Application July16, 1941, Serial No. 402.720

11 Claims.

This invention relates to a method for pro ducing purified granularnitro-aromatic exploslves, particularly nitro-aromatic nitramines suchas trinitrophenylmethylnitramine (tetryl).

The various nitro-aromatic compounds which have been used as basecharges in detonators, and as booster or bursting charges in explosiveshells, bombs, and demolition cartridges must meet rigid requirementsnot only With respect to chemical purity and stability, but also withrespect to handling properties. Thus, before being acceptable for use,each individual nitroaromatic explosive must generally pass tests withrespect to stability, melting point, and absence of foreign material ormatter which is insoluble in a liquid known to be a good solvent for theparticular explosive. In addition, where the explosive is to be handledas a solid, i. e. pressed. into pellets or loaded volumetrically intoshells, specifications generally call for free-flowing qualities of thesolid explosive as well as definite ranges of particle size. It isaccordingly essential that the explosive product should possess bothhigh chemical purity and proper physical form,

The nitro-aromatic compounds which may be used as high explosives aregenerally obtainable by a process of nitrating a suitable interme diatewith the use of mixed acid. The crude material obtained after separationfrom the nitration mixture and thorough washing is characterized by thepresence of of impurities which impair the stability and/or adverselyaiiect other properties such as color, solubility, and melting point.Accordingly, one or more purification treatments are generally requiredfor the obtainment of a product of acceptable purity. Furthermore, ifthe form and size of the particles is not correct at this stage, anadditional crystallization or granulation step must be provided in orderto produce a product which will meet the specified requirements not onlywith respect to purity but also as to physical form.

It has accordingly been extremely difiicult to obtain an entirelysatisfactory product, and, in

the case of tetryl for example, no simple method has heretofore beendescribed whereby the desired granulation and purification can beeffected simultaneously. Thus, when the process employed is that ofcrystallization from a volatile hydrocarbon or chlorinated hydrocarbonsolvent, the solution having previously been washed by agitation withwarm water, the resulting product is characterized by suitable puritybut unsatisfactory handling properties due to improper physical form.Likewise, when the product is prepared by dissolving the crude in asolvent such as acetone and then mixing the solution with Water, theprocess may be carried out so as to result in material havingsatisfactory granulation, but the stability of the product is notconsistently satisfactory.

An object of this invention is to provide an improved simplified processfor the production of stabilized free-flowing tetryl, Intro-aromaticnitramines, or other nitro-aromatic explosives.

Another object of this invention is to provide an improved method forthe granulation of tetryl, nitro-aromatic nitramines, or othernitroaromatic explosives whereby granulation and stabilization areeffected simultaneously.

A further object of this invention is to .provide a method for thepreparation of solid nitroaromatic explosives from solution in anoxygencontaining organic solvent, whereby any deleterious action of thesolvent on the explosive is avoided.

A further object of the invention is the provision of a simple andconvenient method for converting a crude nitro-aromatic explosive into astable free-flowing granular product.

Other objects will be apparent from the following detailed description.

In accordance with this invention, generally stated, a crudeIntro-aromatic explosive is converted into a free-flowing granularproduct having considerably enhanced stability and purity by dissolvingthe same in a volatile oxygen-containing organic solvent, in thepresence of sufficient acid to prevent any deleterious reaction betweenthe explosive and the solvent, and then separating the product from thesolution under conditions controlled to produce the desired granulation.

The method of this invention is adapted for the treatment of theIntro-aromatic explosives such as trinitrotoluene, thepolynitronaphthalenes, tetranitroaniline, and particularly ofnitroaromatic nitrarnines, such as tetryl, and tetryl analogs such astrinitrophenyl-ethyland -butyl-nitramine andhexanitrodiphenyl-ethylenedinitramine (di-tetryl). The material fortreatment may consist, of the crude obtained from the nitration step, orin general of explosive having inadequate stability, purity, or physicalform, such as may result from partial deterioration after extendedstorage.

'In applying this process to the manufacture of tetryl, the crude may beobtained by the nitration of dimethylaniline, but is preferably preparedby the nitration of dinitromethylaniline, obtained for example by theinteraction of 1,2,4-chlorcdinitrobenzene with 1 methylamine, in view ofthe advantages with respect to yield, purity, and ease of nitration inaccordance with the latter method.

The solvent to be employed in accordance with the present procedureconsists largely or entirely of a volatile oxygen-containing organicsolvent, having good solvent propertiesior the explosive under treatmentand which is proferably characterized by complete or substantialmiscibility with water. Ketones, esters, and others, as exemplifiedby'acetone, methylacetate, and dioxan, have been found particularlysuitable, and the solvent for the explosive whether a single orcomposite liquid, should preferably have a boiling point within therange of 40 to 110 (3., although liquids of higher boiling point many attimes be useful.

Oxygen-containing organic liquid solvents are advantageous sincesolutions containing 10%- 50% or more by weight of the explosive canreadily be prepared at convenient operating temperatures by the useeither of an individual solvent chosen from this group or of a suitablesolvent mixture composed largely of one or more members of this group,and a free-flowing granular product is readily obtainable therefrom, asfor example by precipitation of the explosive on mixing the solutionwith a sufi'icient amount of water. However, explosive material preparedin this manner not only fails to meet the requirements of stabilitytests, but frequently displays poorer results than the startingmaterial.

A particularly severe test which is app to nitroaromatic explosives isthe 120 C. vacuum stability test (as described by Farmer in the Journalof the Chemical Society, vol. 117, pages 1432-1445, (1920), in which 5grams of the dry explosive are heated under vacuum for 40 hours, thevolume of gas liberated by the sample during this heating period beingdetermined by measuring the increase in pressure produced within thesystem. A sample which liberates less than 4.0 cc. of gas under theconditions of the test is considered to have a high order of purity andstability, While the evolution of more than 6.0 cc. of gas is consideredto indicate the presence of excessive amounts of deleterious material.extreme sensitivity of this test is indicated by the fact that excessivevolumes of gas may be obtained from samples which would otherwise ap-The I of gas under the conditions of the test.

matter, and by other tests of stability, for example, the Abel test, inwhich a 1.5 gram sample must produce no discoloration of standardpotassium iodide-starch test paper in less than 20 minutes at 99 C.

It has been found that the use of volatile oxygen-containing organicsolvents in the treatment of tetryl leads to a product of suitablephysical form but not having consistently adequate purity as revealed bythe 120 C. vacuum stability test. It has furthermore been found thatrepetition of the treatment produces no improvement in the product inthis respect. Also, attempts to produce an entirely satisfactoryexplosive product by subjecting material of excellent purity but poorphysical form, obtained by crystallization from benzene or toluene, totreatment with an oxygen-containing organic solvent likewise result infailure to obtain a consistently good product.

Further investigation has revealed that the probable cause of theinstability of products resulting from such treatments resides in aninteraction between the explosive nitroaromatic compound and theoxygen-containing solvent, giving rise to, compounds causing theevolution The occurrence of chemical action between the explo sive andthe solvent in such solutions is confirmed by the observation of amarked deepening in color from yellowish-brown to orange or even darkred on standing, which change in color is considerably accelerated by arise in tempera ture and/or in the presence of moisture.

As a result of extensive research, I have discovered that the colorchange can be prevented and a product consistently obtained whichsatisfactorily meets all test requirements, by the precautionofincorporating a sufficient amount of acid with the solvent. A varietyof acids have been found elTective for the purpose, including organicacids such asformic, acetic, tartaric, and salicylic, and inorganicacids such as hydrochloric, sulfuric, phosphoric, and nitric. For eachindividual acid, a minimum ratio to the explosive may readily beestablished by small scale experiments below which effective action isnot consistently obtained, as Well as a maximum ra tio above which nofurther improvement is secured or, in some cases, deleterious action mayoccur. For reasons of economy and because it is essential to remove theacid completely from the finished product, it is preferable to employthe smallest amount of acid which is consistently efiective.

The advantage in using an acidified oxygencontaining solvent, inaccordance with this invention, is apparent from the following tablewhich lists the stability test results obtained on samples of tetryltreated with acidified solvents as contrasted with acid-free solvents. Asolution of tetryl in the indicated solvent was prepared at 40-50 0.;water at -90 C. in the ratio v of 4 parts of. water per part of tetrylwas then pear to be of high chemical purity as judged from meltingpoint, color, absence of insolub e added to the solution during vigorousagitation; and the precipitated tetryl was then filtered, subjected to awashing treatment with water at C., filtered, and dried. In each case,the table indicates the parts by weight of solvent and of acid used perpart by weight of tetryl. The experimental conditions were identical ineach comparison, so that the results indicate directly the beneficialeffect of the presence of acid in the solution of explosive.

Table Gas volume evolved Solvent Acid in 40 hours at None 15 cc. ormore. 0.24 formic. 8.5. 0.20 salicyl 6.9. 0.006pho sphoric. 5.7. 0.00hydrochlo- 4.7.

no. 0. 34sulfuric 4.5. 0.21 nitric 3-6. }None 12 or more.

:1 .1358benzene (or toluene). mmc

.1 acetone .1408methanol g m .1 acetone... r A0 methanol }0.21 nitnc7.%lr2).8 cc. 1n 20 1.58 acetone... g ethyl he }None (1.1 111-20hrs). 1. acetone... I g'thiyl ether }0.21 11ltrlc 20 (6.5 111 20 hrs.).1'. ace one--. J52 acetic mi }None. 12 (4.2 in 20 hrs).

9 (3.1 in 20 hrs).

e }Nonc 1. 6.3.

1 1s acetone-.. blggethyl methyl ketone-- mmc ac one 1% mhylem, glycol}No e so 1 1 0.acone L12 methylene glycol }0.2l nitric 18 (0.9 111 1bhrs). 1.18 acetone .651)- ethylene dichloride one 1. Sacetone .63'ethylene dichloride. 1.18 acetone.. .458ethytl acetate -"f 1.1 ace 0neethyl acetate }0.2l nitric 5.0. 1 87 methylacetate None. 4.9. l 87methyl acetate 0.21 nitric 3.0. 2.17 dioxane None 5.1. 2.17 dioxane 0.21nitric V 2.7 1.65 methyl acetone (20- None 9.3.

25% methanol, 27.531%

mehyl)acetate, 47.5-51% ace one 1.65.1nethyl acetone 0.21 nitric 3.5.

As a further illustration of the striking contrast between the efiect ofan acid-free and an acidified oxygen-containing organic solvent, stabletetryl which evolves less than 4 cc. of gas in the 120 C. vacuumstability test, becomes unsuitable after treatment with the acid-freesolvent such as acetone, liberating a volume of 6 or more cc. of gasunder the 120 test, while a sample of the same material, after beingsubjected to treatment with. the acidified solvent under otherwiseidentical conditions, will still be found to liberate less than 4 cc. ofgas under the test/conditions. 7 V

While, as indicated above, a variety of acids have been shown to beefiective for the purpose,

"""the inorganic acids display greater activity and may be used insmaller proportions than the organic acids. Precautions are required inthe use of hydrochloric, sulfuric, and phosphoric acids in thatproportions in excess of those listed in the above table should not beexceeded, and, in the case of sulfuric and phosphoric acids, thetemperature of the solution of the explosive should be maintained nothigher than about 40 C. Nitric acid is the preferred acid for use in theprocess, in view of the wide range of effective proportions, from about0.05 to 0.40 part of acid per part by weight of tetryl, and the factthat no special precautions are required in its use.

The crude material for treatment in accord ance with the present processmay be in the dry state or it may contain a residual moisture content,for example 8-l5%, which is retained following the final step ofseparating the explosive material from the wash water, as bycentrifuging subsequent to the step of nitration. It is generallypreferable to have the crude as free from residual nitrating acid as canbe accomplished by thorough washing, particularly when the operationsare so carried out that the crude is stored for a period of time beforebeing subjected to the purification and granulation step.

The process of this invention is accordingly applicable for the readyconversion into a product which is satisfactory in all respects from astarting material which is inadequate with respect either to purity orphysical form or both. The material is dissolved to form a 10% tosolution by weight in a solvent which is composed entirely orpredominantly of a volatile oxygen-containing organic solvent at atemperature which is somewhat below the normal boiling point of the.solvent and which is, in any case, not higher I than about 90 C. Typicalpreferred solution temperatures are 40 to 50 C. for acetone or methylacetate; 40 to C. for methyl acetone, and for mixtures predominantly ofacetone with benzene, toluene, ethylene dichloride, or ethyl acetate;and 40 to 90 C. for dioxane or other high-boiling solvents or solventmixtures.

Care is taken to provide sufiicient acid in the solution to prevent anydeleterious action between the explosive and the solvent, for example atleast about 0.05 part by weight of nitric acid per part by weight ofexplosive.

After filtration to insure the removal of any insoluble matter, thesolution is treated to cause separation of the explosive in a highlypurified state and having satisfactory granular form. Preferably theseparation is accomplished by mixing the solution with warm water duringvigorous agitation, under conditions controlled to prevent anysubstantial loss of solvent by volatilization. The explosive is thenseparated from the warm mother liquor by decantation or filtration, isthoroughly washed with warm water to remove the residual acid, solvent,and any other water-soluble constituent, and is then dried to thedesired low moisture content. Another mode of separation of theexplosive consists in cooling the solution to cause crystalliaa% tive"embodiment of the method in accordance with this invention, crude tetrylhaving a deep yellow color and a melting point between 126 and 128 C.obtained by the nitration of dinitromethylam'line with mixed acid, isconverted to a very pure and stable product of satisfactory granularity,pale yellow in color and having a melting point between 128.8 and 129.1C., by the following procedure:

Crude tetryl is dissolved in acidified acetone at a temperature of 40 to50 C. to form a solution containing 1 part by weight of tetryl, 1.3 to1.7 parts by weight of acetone, and 0.05 to 0.25 part of nitric acid,the required amount of acid having been added to the acetone in the formof a concentrated aqueous solution, for example as a to 73% solution inwater.

After filtration of the solution to remove insoluble matter, warm wateris rapidly added thereto during vigorous agitation of the emulsifyingtype. The water, preferably distilled or otherwise treated to have a lowcontent of dissolved solids, is added at a temperature of 55 to C. andin the ratio of about 4 parts by weight of water to 1 part by weight ofthe explosive.

Following a further brief period ofagitation, the tetryl becomessolidified to pale yellow roughly spherical individual particles oragglomerates. These may be separated from the Warm mother liquor byfiltration at about 65 C. on suitable filter beds, and the mother liquormay be treated for recovery of the dissolved-explosive and solventcontent.

The tetryl retained on the filter bed is then subjected to a thoroughwashing with warm water at about 70 to 80 C, in order to remove residualacid, solvent, and other water-soluble constituents. After drying andsieving, the product may be stored ready for use.

Products prepared in accordance with the above procedure invariablydisplay the liberation of less han 6 cc. of gas under the conditions ofthe 120 C. vacuum stability test, and about 4 cc. or less of gas in mostcases. Likewise, the physical form is highly satisfactory, since thematerial is free-flowing and non-dusting, and the size of the individualparticles or agglomerates is largely within the desirable range of 0.006to 0.0336 inch for the largest dimension. The product likewise meets allother requirements with respect to chemical purity and stability.

In accordance with another embodiment, an acidified solution of crudetetryl in acetone, containing 1 part by weight of tetryl, 1.6 partsacetone, and 0.21 part nitric acid, is heated to 50 C., and addedrapidly during vigorous agitation to 4 parts by weight of Water at 85 C.contained in a closed vessel. Following a brief period of vigorousagitation, the crystallized tetryl is separated from the mother liquoras by filtration, thoroughly washed with warm water, and dried. Themother liquor may be treated for recovery of its content of explosiveand solvent. The tetryl product consists of individual short thickcrystals characterized by very favorable free-flowing and non-dustingqualities and by exceptional purity and stability in accordance with theknown tests, evolving from 1.1 to 2.5 cc. of gas, averaging about 1.75cc., during the 120 C. test.

The washing, treatment following filtration may conveniently be carriedout by suspending the tetryl in warm water, heated to a temperature of'70? to 80 (7., for 3 to 4 hours with one intermediate change of waterafter 1 to 2 hours. This treatment when applied following'the treatmentwith acidified oxygen-containing solvent has been found to reduce thevolume of gas liberated during the 40 hour 120 C. test by 1 to 2 cc.Below 70 C., the purification action is too slow while above 80 C.,hydrolysis of the tetryl sets in, impairing the quality of the product.This extent of improvement in the final product .by means of this typeof final hot water washing treatment is not obtainable when the priorprocessing treatment has been effected by means of an oxygen-containingsolvent free of acid.

A particularly favorable tetryl product may be obtained by the use ofacid in a -50% Solution of tetryl at a temperature above 40 C. andmixing with water at a temperature above 50 0., all at atmosphericpressure, in accordance with the procedure disclosed and claimed in theco-pend- ,ing application of Delbert R. Jones, Serial Number 402,718,filed July 16, 1941, whereby the explosive is initially separated as aliquid phase which persists for some time and subsequently becomessolidified into solid granules or agglomerates. The solid explosive isthen advantageously given a thorough washing with water, as describedabove, and dried.

It is to be understood that this invention is not limited to the detailsof procedure hereinbefore specifically described for the purpose ofillustration but that variations and modifications may be made withoutdeparting from the spirit thereof, and that such variations andmodifications are, although not specifically described herein,contemplated by and within the scope of the appended claims. The termoxygen-containing organic solvent, as used herein, refers to a sol ventconsisting entirely or predominantly of one or more organic liquids inwhich at least one oxygen atom forms an integral part of the molecule.

Having now described the invention, what is claimed as new and isdesired to be secured by Letters Patent is: Y

1.'In themanufacture of explosives, the process comprising preparinga-10-% to 50% solution of a nitro-aromatic explosive in a volatileoxygencontaining lorga'nic solvent normally reactive therewith toimpair'its thermal stability, said solution containing 0.05 to 0.25 partof nitric acid per part of the said nitro-aromatic explosive to inhibitsuch deteriorating effect, and mixing said solution with'water toseparate the said explo- SlVe; Y

2. In the manufacture of explosives, the proc ess comprising preparing a10% to 50% solution of a nitro-aromatic nitramine in a volatileoxygen-containing. organic solvent chosen from the group consisting ofketones, sters, and ethers, said solution containing 0.05 to 0.25 partof nitric acid per part of the said nitro-aromatic nitra-f mine toinhibit such deteriorating effect, and mixing said solution with waterto separate the said nitramine.

3. In the manufacture of explosives, the process comprising preparing a10% to 50% solution of tetryl in a volatile oxygen-containing organicsolvent chosen from the group consisting of ketones, esters, and ethers,said solution contain; ing 0.05 to 0.25 part of nitric acid per part ofthe said tetryl to inhibit such deteriorating effect, and mixing saidsolution with water to separate the tetryl. v

4. In the manufacture of explosives, the process comprising preparing a10% to 50% solution of tetryl in a volatile oxygen-containing organicsolvent chosen from the group consisting of ketones, esters, and ethers,said solution containing 0.05 to 0.25 part of nitric acid per part ofthe said tetryl to inhibit siich deteriorating effect, mixing saidsolution with water to separate the tetryl, and washing the separatedtetryl with water ata temperature of 70 to C.

5. In the manufacture of explosives, the process comprising preparing asolution of a intro-aromatic explosive in acetone, said solutioncontaining 0.05 to 0.25 part of nitric acid per part of explosive, andmixing said solution with water to separate the said explosive.

6. In the manufacture of explosives, the process comprising preparing asolution of a nitro-aromatic nitramine in acetone, said solutioncontaining 0.05 to 0.25 part of nitric acid per part of explosive, andmixing said solution with water to separate the said nitramine.

7. In the manufacture of explosives, the process comprising preparing asolution of tetryl in acetone, said solution containing 0.05 to' 0.25part of nitric acid per part of tetryl, and mixing said solution withwater to separate the tetryl.

8. In the manufacture of explosives, the process comprising preparing asolution of tetryl in acetone, said solution containing 0.05 to 0.25part of nitric acid per part of tetryl, mixing said solution with waterto separate the tetryl, and washing the separated tetryl with water at atemperaof the said explosive and a minor proportion of an added acid ina volatile oxygen-containing organic solvent chosen from the groupconsisting of ketones, esters, and ethers, and mixing said solution withwater to separate the explosive.

11. In the manufacture of explosives, the process comprising thoroughlywashing a nitro-aromatic explosive with water, preparing a solution ofthe said explosive and a minor proportion of an added acid in a volatileoxygen-containing organic solvent chosen from the group consisting ofketones, esters, and ethers, solidifying the explosive from the saidsolution, and thoroughly washing the solidified explosive with water.

JEROME G. BURTLE.

CERTIFICATE OF CORRECTION. Patent No. 25 L660. May 2, 191m.

JEROME G. BURTLE.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 1,first column, line 52, for the words "presence of of" read presenceof--; page 2, first column, line 59, for "many" read may-; page L;.,first column, line 17, for "han" read -than; and second column, lines 21and 22, claim 1, for "normally reactive therewith to impair its thermalstability" read -Chosen .from the group consisting of ketones, esters,and ethers-; lines m" I 'H 2b. and 25, same claim, line 55, claim 2,line 1414., claim5, and lines 55 and 51+, Claim l strike out "to inhibitsuch deteriorating effect"; and that the said Letters Patent should beread with this correction therein that the same may conform to therecord of the case in the Patent Office.

Signed and sealed this Lyon day of July, A. D. 19th.

Leslie Frazer (Seal) Acting Commissioner of Patents.

CERTIFICATE OF CORRECTION. Patent No. 2,5h7,660. 4 May 2, 191m.

JEROME G. BURTLE.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 1,first column, line 52, for the words "presence of of" read -presenceof-; page 2, first column, line 59, for "many" read -may; page L, firstcolumn, line 17, for "han" read than-; and second column, lines 21 and22, claim 1, for "normally reactive therewith to impair its thermalstability" read chosenfrom the group consisting of ketones, esters, andethers; lines 21; and 25, same claim, line 55, claim 2, line M claim 5,and lines 55 and 5b., claim 14., strike out "to inhibit suchdeteriorating effect"; and that the said Letters Patent should be readwith this correction therein that the same may conform to the record ofthe case in the Patent Office.

Signed and sealed this hth day of July, A. D. 19%.

Leslie Frazer (Seal) Acting Commissioner .of Patents.

